A conventional dead bolt door lock is constructed so that it can incorporate any of a large variety of interchangeable externally threaded lock cylinders that are commercially available from a variety of sources. On the inner end of the cylinder, an eccentric cam is rotatably mounted, and a linkage must be provided that causes recipricatory movement of a bolt between retracted and extended positions in response to movement of the cam.
A wide variety of arrangements for transmitting the motion of the cam to the bolt have been proposed. One important requirement has been that relatively strong and heavy components must be used, enabling the bolt to withstand any effort to disable the lock by driving it forcefully back toward its retracted position. These connecting components are not only costly, but they sometimes make the lock difficult to operate, offering high resistance to bolt movement.
Another important disadvantage of conventional dead bolt locks is that it is generally possible to rotate the cam in the wrong direction through a large angle, sometimes approaching a full turn. This makes the operation of the lock confusing, particularly where there are several locks on a single door so that it is difficult for the user to determine whether he or she has properly actuated the bolt.
Another disadvantage of a conventional dead bolt is that the key must be rotated in a first direction, and then counterrotated, thereby returning to its original position so that it can be withdrawn. In many cases, the user does not rotate the key through a large enough angle to fully extend the bolt before counterrotating and removing it. The result is that the bolt remains in a partially extended position and the door has the appearance of being locked, but the bolt offers almost no resistance if pushed toward its retracted position by an external force.
A principle objective of the present invention is to provide an improved dead bolt lock that overcomes the above-mentioned operational disadvantages of conventional locks. A further objective is to provide such a lock that is particularly well suited for relatively inexpensive lightweight construction and offers a minimum resistance to operation without sacrificing the strength of the lock.